The project objective is to identify maternal nutritional and nutritionally-related hormonal effects on the transplacental flux of amino acids, glucose, and lactate, and to define the mechanisms of regulation of fetal nutrient availability and the subsequent effect of such regulation on fetal growth. The study will be conducted in pregnant sheep which have been surgically prepared with catheters in fetal vessels. The animals will be allowed to recover from the stress of surgery before investigating the effects of maternal nutritional alterations on umbilical substrate uptake. The study is relevant to clinical perinatal medicine in that it seeks to unravel the pathophysiology of intrauterine growth disturbances.